We are proposing to study two specific tRNA changes which occur when a lens epithelial cell differentiates into a lens fiber cell. One of these involves a specific decrease of one isoaccepting lysine tRNA. This causes a decrease in the ability to read the codon AAG with no corresponding decrease in the ability to read the codon AAA. The other involves the formation of a novel species of phenylalanine tRNA which is similar to, but not identical to, the major phe-tRNA in lens tissue. These tRNAs will be isolated, assayed for modified base content and tested for their ability to incorporate amino acids into lens specific proteins.